A collection of pixels is modulated for displaying an image on a digital display, a pixel is either in an `on` condition or in an `off` condition. For example, the `on` condition can represent white and the `off` condition can represent black. To provide more information and realism in the image, it is generally desired to provide intermediate intensities or greyscale levels. Pulse width modulation (PWM) is a well known technique for achieving intermediate greyscale levels. According to PWM, the pixels are rapidly toggled a varying portion of the time between `on` and `off`. The larger the percentage of time the pixel is `on`, the closer to white the pixel is displayed. Assuming the clock rate is sufficiently fast, a viewer's eye integrates the intensity of a toggled pixel to perceive grey rather than merely black or white. The intensity level for the pixel depends upon the relative durations of the `on` state and the `off` state. It is well understood that pulse-width modulation can also be applied to color systems for forming varying intensities and shades of color.
Digital display systems generally include a plurality of pixels arranged in an array of rows and columns. Conventionally, a row of image data to be displayed is loaded from a video memory into a shift register and then utilized to pulse-width modulate each pixel in a corresponding row of a display panel according to the data in the register. Modulation for each row of pixels is generally performed in a regular sequence beginning with a left-most pixel in the row and ending with a right-most pixel. Once the row is complete, image data for a next row of pixels is loaded into the register. According to prior art systems, this process repeats for each row in the display, thus, forming a complete frame. Once the frame is completed, the image is continually updated by repeating this process.
A drawback to this conventional display system is that because the pixels are modulated in a regular sequence and in the order in which they appear in the display, the updating process can induce false motion artifacts into the image. For example, lines can appear to move in the image or the image can appear to flicker, especially in the presence of fluorescent lighting systems.
What is needed is a technique for updating a digital display system with image data according to a pulse-width modulation technique that does not induce motion artifacts into the image.